Inside shoe drum brakes are used in hydraulic brake installations for passenger cars and commercial cars as two-shoe drum simplex brakes. It is a known problem of such inside shoe drum brakes that during operation the brake shoes are abutted against the brake drum, and an unpleasant operating noise develops, the so-called brake squeal. In the state of the art, there have been many attempts to reduce or to eliminate brake squeal by special construction designs of the inside shoe drum brake.
Thus, from German Patent Publication DE-AS 1,103,160 an inside shoe drum brake is known with a brake anchor plate to which contact plates are attached which form flat contact surfaces extending perpendicular to the brake axis, for the inside lateral surfaces of the brake shoes which are pivotally supported with respect to the brake anchor plate. A bolt which is attached to the brake anchor plate passes through each brake shoe bar. Between the lateral surfaces of the brake shoe bars, which are turned away from the brake anchor plate, and the bolt ends, a pressure spring is arranged on each bolt, which biases the respective brake shoe in the axial direction against the corresponding contact plate. The result is that the brake shoes with their interior lateral surfaces are always firmly braced against the contact plates, so that an oscillating of the brake shoes and a corresponding excitation of the brake drum are avoided.
Further, it is known to provide, on the brake anchor plate (U.S. Pat. No. 3,177,978) or on the brake shoes (U.S. Pat. No. 3,220,515), a plurality of small bearing blocks made of a material with low coefficient of friction, which brace the brake shoes which are biased by means of springs in the direction of the brake anchor plate, on their interior lateral surfaces with respect to the brake anchor plate, to avoid oscillation of the brake shoes.
Furthermore, the generic German Patent Publication DE 4,203,173 A1 discloses an inside shoe drum brake with a bearing block for receiving the circumferential forces of the brake shoes which can be pressed by means of a hydraulic wheel brake cylinder against the brake drum, and a brake anchor plate which carries the bearing block and the wheel brake cylinder and which comprises an area for the attachment of the brake to a wheel carrier.
According to this state of the art, the brake anchor plate is constructed in a sandwich pattern using two plate parts with different material thickness, of which the first plate part which can be attached to the wheel carrier has a larger material thickness and carries the bearing block for the brake shoes, whereas the second plate part has a smaller material thickness and serves for the attachment of the wheel brake cylinder. The second plate part has several contact surfaces and small plates, respectively, made of a material which allows sliding, against which the brake shoes which are biased by means of springs in the direction of the brake anchor plate are held in contact with their interior lateral surfaces, or two curved brace areas which are axially projecting in the direction of the brake drum and which are provided with a covering which can slide, and with which the biased brake shoes are in contact with their bars.
Although, according to the above-described state of the art, a decrease in brake squeal can be obtained, the problem common to this state of the art is that relatively many individual parts are required to improve the noise behavior, which parts in addition must be mounted with correspondingly high effort.
Finally, an inside shoe drum brake is known from German Patent Publication DE 2,903,051 A1 which has a brake anchor plate with larger material thickness. The brake anchor plate has several arms which extend radially, one of which forms the housing of the wheel brake cylinder, whereas the other arms comprise at their ends guide slits into which U-shaped spring clamps are inserted, which serve to axially guide the brake shoes on their bars.
In this rigid design of the brake anchor plate, a good overall noise behavior of the inside shoe drum brake can certainly be expected, however, such a brake anchor plate cannot be manufactured economically because, on the one hand, it must be cast in molds with associated spoiled casting, and, on the other hand, the formation of the guide slits requires an additional work step.